Remove beam-mapping opt eff stuff.

The results from this analysis were clearly too low, and not
compatible with the results from IV curves. So I'm removing them and
will replace with IV curve results.
Rewrite optical efficiency section.
Notes on how to handle distance discrepancy
Added text about foil window test.
Merge branch 'master' of github.com:danbek/thesis
Updates for correct distance mapping.
Correct temperatures for dime maps
Fix temperature scale for still images
Fix temperatures for single-frame plot.

Also use png files to create images.